1. Field of the Invention
The invention pertains to the field of DC power supplies. More particularly, the invention pertains to methods and apparatus for control of loads on DC power supplies.
2. Description of Related Art
In many electrical systems DC power is applied to a load (or loads) by a DC output power converter or a DC switch at the assertion of an on-off control signal or simply by applying power to the input of the DC switch or the DC output power converter. When power is removed to these devices or the device is commanded to turn off, stored energy within their load(s) dissipates passively due to energy consumption or other parasitic losses within the load. Generally, no effort is made on the part of the DC switch or DC output power converter to remove this stored energy from the DC load. In fact, DC output power converters are often designed to sustain their output as long as possible so they can deliver seamless power to their load(s) even when there are short power outages. (Within the power supply industry the ability to do this is specified as “hold-up time”.)
In contrast, in certain applications, it would be an improvement not only to rapidly interrupt energy flow to DC loads, but to also remove stored energy from within the load(s) as soon as possible. Today, this is accomplished by means outside the power source: adding brakes to mechanical loads, passively draining current from capacitors, etc. These techniques require additional expense and complexity on the part of the user and/or add to the system energy losses while operating.
There is a need for DC output power converters and DC power switches to remove energy from their loads when power is removed from their inputs or they are switched off. This would be especially useful when loads contain motors moving mechanical elements that need to be brought to a halt to protect mechanics and human operators when power is removed or shut off. It's also important when the charge on capacitors within a load represents a shock and/or energy hazard (e.g., which are exposed when an interlock switch shuts off power when a guard is removed). Where human safety is concerned, such an energy removal apparatus would also benefit from fault tolerant operation, possibly using more than one energy removal method.